Quenching of heated glass sheets on roller conveyors such as for tempering or heat strengthening is difficult to perform because the conveyor rolls that support the glass sheet for conveyance obstruct the lower glass surface. As such, there is limited area for permitting the jets of quenching gas to impinge with the lower glass sheet surface and for the spent quenching gas to flow downwardly away from the glass sheet after impingement with the glass sheet. Furthermore, the presence of the conveyor rolls below the plane of conveyance provides a different quench configuration than above the plane of conveyance such that the lower and upper glass sheet surfaces are not quenched symmetrically to each other.
In order to accommodate for the conveyor roll obstruction problem at the lower glass sheet surface, it is conventional as disclosed in U.S. Pat. No. 4,515,622 McMaster et al to provide quenching gas outlets that are spaced from the glass sheet a distance at least as great as the conveying diameter of the conveyor rolls. Angling of quench tubes through which the quenching gas is supplied as disclosed by the McMaster et al patent permits a greater number of locations of impingement to be provided without blocking the area through which the spent quenching gas flows downwardly away from the conveyed glass sheet after its impingement with the adjacent glass sheet surface.